Radio



June 21, 1932. FRANc|$ 1,863,568

RADIO Filed Dec. 17, 1928 Ba 1 AC Filamenf Supply L13 Ra B6 II Zhueni'or: Qliuer 27 Ikancis,

Patented June 21, 1932 OLIVER '1. FRANCIS, OI" QUANTICO, VIRGINIA.

RADIO Application filed December 17, 1925. Serial R0. 320,050.

This invention relates to regulators of electric current and potential and more part1cularly to the regulation of differences of potential between the elements of a vacuum tube One object of the invention is to automatlcally control theoutputof a vacuum tube amplifier in such a manner as to cause it to discriminate against input energy of a value above or below a predetermined value, causing said input energy not to appear in the output circuit, or to e of greater value than the input energy of the desired value. P nother object is to cause extremely loud signals such as crashes of static to be eliminated from the output circuit of said amplifier and signals which ordinarily cause blasting in the ordinary receiver to be no louder than signals of less magnitude impressed on said amphfier. Another object is to provide an automatically variable grid leak which shall keep the static grid potential of a vacuum tube amplifier at a constant value regardless of the strength of the incoming signal. Another objectis to provide a circuit in the output circuit of a vacuum tube amplifier; in which virtually no current shall flow until a certain predetermined voltage is impressed on the grid of same at which time a considerable amount of current shall flow in said circuit.

A still further object is to place the present means of manual control of vacuum tube amplifiers under automatic control by means of regulating the impedances across is e input or output thereof, and of regulating the heat of the filament thereof.

With these and other objects in view the invention may be more fully understood by reference to the following description in connection with the drawing which shows diagrammatically several of the embodiments of the invention.

Figure 1 shows a single stage amplifier employing in accordance with the invention a variable impedance element as grid leak.

Fig. 2 shows a means of varying the impedance of the element inversely in accordance with the envelope of the strength of the incoming signal.

Fig. 3 illustrates how the princi Ice involved may be utilized to control t e heat of the filament of the amplifier.

Referring to Fig. 1 we find the vacuum tube V1 coupled to t eprevious stage of amplification V by means of R1. Instead of a grid leak of the ordinary type the primary P1 of a transformer L1 has been used. In the secondary S1 of this transformer has been inserted a variable resistance N1, which has 5 the ,icharacteristic of possessing a very high resistance until a certain voltage is impressed thereon at which time it has a very small resistance. Such a resistance is a Geissler tube,

a neon lamp, a voltage regulator tube, a small spark gap. The primary of this transformer, which in the present lnstance is a step up transformer has a high impedance to alternating current impressed on the grid of V1. If due to a strong incoming signal the grid of V1 would tend to become negative as is the case with ordinary grid leaks with resistance coupled amplifiers when a strong signal is received, the impedance of L1 would become small, since the voltage induced, in the secondary of this transformer would break down the resistance of N1. Thus we find that the grid of this tube is maintained at a constant static potential with respect to the filament and modulation which occurs with resistance 39 or impedance coupled amplifiers is impossible. In the case of transformer coupled amplifiers it is obvious that the resistance N1 could be placed directly between the grid and filament with similar results.

Fig. 2 shows a method of varying the impedance of the grid leak of V inversely in accordance with the envelope of the strength of the incoming signal, impressed upon the primary P of transformer L. The rimary P of the transformer L -is here per orming the function of a variable grid leak. In the secondary S of the transformer is inserted an element N In parallel with N is the element R which is a high fixed resist- 06 I ance. The tube V is coupled to the previous stage of amplification. On the grid of V is impressed a suificiently great negative voltage so that very little current will flow in the output circuit of this tube when ordinary l signals are being This small current will not cause an IR drop across R sufficiently great to break down the neon lamp.

C1 keeps the direct current from V3 from flowing through the secondary S of L. A filter system consisting of Z1 and C2, similar to that used in ordinar battery eliminators has been inserted to c ange the pulsating current which comes through V to direct current. When, however, a strong incoming si al is received, such as that caused by a crasi of static or'local disturbance, the impedance of V will greatly decrease. This will cause a ater voltage to be impressed on B2 and 1%? The resistance of N2 will then break down and become very small. Since in this instance the grid and filament are virtually shortcircuited the crash will not be recorded in the output circuit of V2.

It is obvious that a device similar .to the one described in the preceding paragraph could be laced across the output circuit of the tube thereby shortcircuiting the plate and filament, with similar results. Also that the plate and grid of the tube could be shortcircuited by a similar device, lacing the resistance and the neon lamp tween these elements and inserting small condensers to keep the direct current from V3 011' the plate and grid V2.

By referring to Fig. 3, we find that the principles illustrated above may be used to regulate the heat of the filament of the amplifier. Transformer L3 is across the A. 0. current filament source of supply of the vacuum tube V4. In the output circuit of supplemental or auxiliary tube V is inserted high resistance R and neon tube N and secondary S of transformer L. When the signal impressed on the circuit exceeds a predetermined limit the secondary S of this transformer is virtually short-circuited through neon tube N in accordance with principles described above, thus decreasing the in uctance of the primary P and decreasing the heat of the filament of V. The resistances R3, preferably resistances with a positive temperature coeflicient, have been inserted in the A. G. lines to cause the desired IR drop when the increased demands for current are made due to the decrease of impedance of the primary P of L.

The principles above described may be aplied to circuits where the filament supply is irect current, by inserting the resistance in series with the filament supply current and varying the resistance of such elements, the

II} drop across same, or both, in accordance with the principles already described.

It is rther apparent that the general principles dlsclo may be embodied in It will be understood where vacuum tube am lifier is referred to in the claims it will inc ude within its meaning thermionic tube am lifier or any equivalent tube amplifier.

be broad principle of my invention may be stated to be the method of automatic control of amplifying or rectifying, or other electrical circuits, consistin in rectifying or amplifying a portion of the input current and applying said rectified or amplified portion to an element in the secondary of a transformer, thereby varying the resistance of said element, thereby varying the impedance of the secondary of the transformer, thereby var ing the impedance of the primary of said transformer, and thus controllin automatically the voltage drop across said primar hat is claimed is:

1. In a vacuum tube am lifier set, a vacuum tube amplifier, a grid eak consisting of the primary of a transformer, an elementin the secondary ofsaid transformer which becomes highly conductive to electricity when a predetermined voltage is impressed thereon, and means for producing said predetermined voltage b rectifying a portion of the input energy 0 said set thereb virtually short-circuiting signal voltages a ove a redetermined valve from the grid to the lament of said tube.

2. In a vacuum tube amplifying system, means for discriminating against in ut energy above a predetermined value, sai means comprising means for rectifying a portion of said input energy and for applying the rectified portion of said ener to a gas conducting tube, connected in t e secondary of a transformer, to render the said gas conducting tube conductive, the primary of said transformer being connected as a grid leak of one of the vacuum tubes of said amplifying system.

In testimony whereof, I aflix my si ature.

OLIVER T. FRA CIS.

many organizations widely different from thom illustrated without departing from the spirit of the invention as defined in the following III 

